This publication presents an experimental study which was conducted to examine the effects of various types of environments on the flexural stress and load-deflection relationships of the composite cantilever beams subjected to a single force at their free end for different exposure times. The study includes the testing of five different conditions which are cold, hot, humid, seawater environments and room temperature. Maximum flexure stresses and deflections of cantilever beam are presented analytically, numerically and experimentally. ANSYS FEA program is used for numerical analysis of composite materials. The test results carried out after generally one and two months of exposure to the different environmental conditions show that the flexure stress and deflection of the beams are affected at different levels. Moreover, it is shown that the analytical and numerical results are consistent with the experimental data.